1. Field of the Invention
The present invention relates to a cathode ray tube (CRT) used as, for example, a color television or a display device for an information processing terminal device, and a method of manufacturing the CRT. The present invention also relates to a color selecting member for a CRT, for ensuring that an electron beam strikes a predetermined position in a phosphor pattern, and a method of manufacturing the color selecting member.
2. Description of the Related Art
A CRT is used as a usual type of color television receiver of the related art or a display device for an information processing terminal device. For the purpose of achieving a CRT of high picture quality by solving problems such as a chromatic blur of neighboring color pixels, there is provided a color selecting member such as an aperture grille or a shadow mask. Such a color selecting member is used for exposure to form patterns for respective color phosphors in a self aligning manner. Based on the patterns formed by exposure, phosphor patterns corresponding to respective color pixels are formed by photolithography or the like.
In recent years, the size of a screen, especially in a color television receiver, has been increasing. On the other hand, a color television receiver adapted to a high definition display system, what is called a HDTV (high definition television) system, is being developed and put into practical use. Enlarging the entire screen in such a color television receiver involves an increase in the size of the entire CRT.
In the case of a CRT for HDTV, since its screen is further widened especially in the lateral direction (horizontal scan direction), the size of the CRT in the lateral direction is remarkably increased. The CRT for HDTV has to therefore provide for upsizing especially in the lateral direction (horizontal direction). On the other hand, since the CRT for HDTV is a display device for the purpose of higher picture quality in a high definition display system, the CRT for HDTV requires higher picture quality while upsizing.
In such a CRT of the related art, especially a color selecting member and a phosphor layer are manufactured in the following manufacturing process.
FIG. 5 is a schematic diagram showing a process of exposure to form a phosphor layer in a process of manufacturing a usual single-gun type of CRT of the related art. The Description given below relates to the case of a CRT using a phosphor pattern in vertical stripes and a color selecting member (that is, aperture grille) of the related art.
Referring to FIG. 5, a photosensitive agent (not shown) such as resist is applied to the inside of a front panel 1. A color selecting member 2 is mounted just behind the front panel 1. The color selecting member 2 has narrow slits or a number of rectangular holes arranged in a slot pattern or in a dot pattern. Then, the front panel 1 is exposed through the color selecting member 2 so as to form a pattern for carbon stripes having predetermined widths and pitches in predetermined positions. After that, carbon is applied and dried, and the stripes of the photosensitive agent are removed with a chemical (or a solvent) such as hydrogen peroxide, thereby forming carbon stripes.
A film made of a mixture of each color phosphor, namely, for example, R (Red), G (Green) and B (Blue), and the photosensitive agent is formed and exposed with the exposure position shifted so as to form a pattern in vertical stripes having predetermined widths and pitches in predetermined positions. The pattern formed by exposure is used to form stripes (not shown) of each color phosphor by photolithography. Thus, a phosphor layer is completed.
When the CRT is used as a completed product in practice, an electron beam emitted from an electron gun strikes accurately its intended area in the phosphor layer formed as mentioned above. Thereby, the color phosphor at the intended position emits light and is observed as a pixel. In order to attain high picture quality, the phosphor has to be formed in an exact position where the electron beam strikes. In other words, a deviation of the phosphor from the exact positioning causes defective display such as misregistration, which deteriorates picture quality severely. The demands on exact positioning of the phosphors are becoming even severe in order to cope with higher definition attained in recent years.
For the purpose of accurate positioning of the light for exposing a phosphor and the electron beam, provided is a correction lens system 4 between a light source 3 of a projection aligner and the front panel 1 (more concretely, the phosphor layer). Thereby, a deviation between the locus of the electron beam and that of the light for exposure is corrected. The correction lens system 4 has an uneven shape in cross section as shown in FIG. 5.
In recent years, while the size of the screen is increasing as described above, reduction in a depth dimension has been strongly demanded in the outer shape of the entire television receiver. Since there is a tendency that the size of the entire CRT has to be increased as the size of the screen increases, the depth dimension of the CRT tends to increase. That is, it goes counter to the demand on reduction in a depth dimension of the outer shape.
Particularly in the case of a CRT adapted to a large screen, especially a CRT for HDTV of a wider screen, further reduction in a depth dimension of the CRT is almost impossible in the single-gun type of CRT. Thus, as shown in FIG. 6, there has been a proposal for a CRT in which two or more electron guns 5 are arranged side by side in the lateral direction. The electron guns 5 are housed in the respective necks 7 of the respective rear funnels 6. Deflection yokes 8 are provided around the respective necks 7 in correspondence with the respective electron guns 5.
The use of a plurality (two in this case) of electron guns 5 in side-by-side arrangement as mentioned above enables an electron beam emitted from each electron gun 5 to move across only about half of the screen. This enables an electron beam to strike especially in the peripheral areas of the screen at a reasonable angle, even if a depth dimension is reduced by shortening the distance between the electron gun 5 and the front panel 1. Thus, a depth dimension of the outer shape is reduced while being adapted to the large screen. In addition, high picture quality can be achieved throughout the entire large screen.
Since a usual type of CRT of the related art has one electron gun 5, a projection aligner used in the manufacturing process also adopts a system in which one light source corresponds to one front panel.
FIG. 7 shows a CRT for large HDTV, as an example of a large CRT having an extremely wide screen, during the process of exposure to form a phosphor layer by using a usual type of projection aligner of the related art having only one light source system 3 in only one place. The portion in FIG. 7 denoted by reference character A is shown in FIG. 8 in enlarged dimension. As seen from FIG. 8, the use of a usual type of projection aligner of the related art causes a considerable deviation of the locus of light 9 for exposure and that of an electron beam 10 from each other.
The reason is as follows. The number of electron guns for emitting the electron beam 10 is two while there is provided one light source system 3. This causes a large difference between the incident angle of the electron beam 10 and that of the light 9, which pass through the same single hole 11 in the color selecting member 2. As a result, there is a considerable deviation of the position of each color phosphor or each pixel phosphor formed in the photolithography process including the exposure process using the light 9 from the position where the electron beam 10 strikes. This produces problems of deterioration in picture quality and occurrence of display failure.
One possible method to cope with the problem may be, as shown in FIG. 9, to modify the projection aligner for the manufacture of the multiple-gun CRT by adapting to the number of the electron guns and their disposing positions in the CRT to be manufactured.
It is, however, impossible to adopt such a method in practice by using the existing exposure stage as it is. Either the existing exposure stage is extremely largely modified or a new projection aligner has to be manufactured. This causes an increase in manufacturing cost. Moreover, in the case of taking the trouble and manufacturing a projection aligner having a plurality of light sources 3, the structure becomes more complicated than the related art structure. High precision in positioning is required in the joint area of the phosphor layers formed by using the respective light sources 3. Thus, high accuracy of the projection aligner itself is strictly demanded, causing a problem that the manufacture and handling at the time of operation in the exposure process, and so on are complicated.
To be specific, when light from the light sources 3 in two places as shown in FIG. 9 is emitted for exposure, the two areas irradiated by the light from the respective light sources are joined in a central part 12 of a screen. This requires extremely precise control of the alignment (positioning) at the time of exposure in the joint part.
In the CRT, however, as is outstanding especially in the case of the HDTV or the like, the definition is becoming higher and the number of pixels is further increasing. Consequently, there is a problem of an extremely high probability that the phosphor patterns are deviated in position or deformed in the joint area of the two areas exposed to the light from the respective light sources.
Specifically, it is known that when the position of the light source 3 is deviated by 0.1 mm, the position of the phosphor pattern is deviated by about 5 xcexcm. The deviation of 5 xcexcm with respect to the size of pixels of high density achieved in recent years is observed as relatively serious misregistration on a screen in actual use, as compared with the size of one pixel. This problem becomes even more serious if the positional deviation or deformation of the phosphor patterns occur in the joint area at the time of exposure, resulting in a conspicuous deterioration in picture quality in the central area of the screen of the CRT. This causes a critical defect in a display device.
In order to prevent the occurrence of defects in the joint area at the time of exposure, not only higher accuracy in mounting the light source 3 or machining the correction lens 4 but also closer control on the dimensional accuracy of the entire projection aligner are necessary. This causes a problem that the manufacture of the projection aligner, handling at the time of the operation of the projection aligner, and so on become very complicated.
Furthermore, since the joint area is irradiated with the light 9 from both of the two light sources, the photosensitive agent such as resist in the joint area is exposed double as compared with the photosensitive agent in the other area. Consequently, there is an extremely high probability that the patterns in the joint area are of different shapes and dimensions from those in the other area. This results in a problem that the pixels in the joint area, as distinct from those in the other area, are observed as display failure or defective display.
The present invention has been achieved in consideration of the problems. An object of the present invention is to provide a cathode ray tube and a method of manufacturing the cathode ray tube, and a color selecting member for use in the cathode ray tube and a method of manufacturing the color selecting member, which can be manufactured without a defect by using an existing simple structured projection aligner and can always produce a picture of high quality by solving a problem of occurrence of display failure or defective display due to relative deviation of the positions of an electron beam striking a phosphor at a certain incident angle, a hole or a slit in a color selecting member for allowing the electron beam to pass through, and a phosphor.
A cathode ray tube of the present invention comprises: an electron gun for emitting an electron beam for scanning; a panel disposed so that a back side of the panel faces the electron gun; a color selecting member which is disposed between the back side of the panel and the electron gun, has a slit elongated in the same direction as the longitudinal direction of the outer shape of the panel, and allows the electron beam for scanning to pass through the slit; and a phosphor layer which is provided on the back side of the panel and has a pattern in stripes corresponding to the shape of the slit in the color selecting member so as to be irradiated with the electron beam passed through the slit in the color selecting member.
A method of manufacturing a cathode ray tube of the present invention comprises steps of: forming a phosphor material layer on the back side of a panel on which a picture is produced; mounting behind the panel a color selecting member having a slit elongated in the same direction as the longitudinal direction of the outer shape of the panel, and forming a phosphor layer having a pattern in stripes in the same direction as the longitudinal direction of the outer shape of the panel by patterning the phosphor material layer using the color selecting member as a mask.
The slit in the color selecting member for the cathode ray tube of the invention has a shape elongated in the same direction as the longitudinal direction of the outer shape of the color selecting member.
According to the present invention, a method of manufacturing a color selecting member for a cathode ray tube comprises steps of: forming a photosensitive material layer on a material for forming the color selecting member for the cathode ray tube; exposing the photosensitive material layer by irradiating the photosensitive material layer with light from a light source in one place to form a latent image of a slit pattern on the photosensitive material layer, the slit pattern elongated in the same direction as the longitudinal direction of the outer shape of the color selecting member for the cathode ray tube; and forming a slit elongated in the same direction as the longitudinal direction of the outer shape by developing the latent image of the slit pattern and patterning the material based on the slit pattern.
In the cathode ray tube or the method of manufacturing the cathode ray tube according to the present invention, the slit in the color selecting member is elongated in the longitudinal direction of the color selecting member itself. That is, the slit is elongated in the longitudinal direction of a display panel, while a display panel is generally in landscape orientation. In the meantime, the stripe pattern of the phosphor layer is formed so as to correspond to the shape of the slit in the color selecting member.
As a result, even in a case where there are a plurality of electron guns for emitting electron beams and one light source system of light emitted at the time of exposing the phosphor, as distinct from the related art, no deviation occurs between the position of the phosphor and the actual position irradiated with the electron beam. This enables exposure using only one light source (in one position). No joint areas or the like are formed on the screen by light sources at the time of exposure, eliminating a problem such as a positional deviation.
The color selecting member has only the slit elongated in the same direction as the longitudinal direction of the. outer shape of the color selecting member. There are no vertical patterns which substantially disturb passage of electron beams in the slit extending from the right end to the left end across the screen. Even in case of a considerable horizontal deviation due to, for example, the thermal expansion of the color selecting member, the electron beam passes through the slit elongated horizontally, and the accuracy of irradiation of the phosphor with the electron beam is not adversely influenced. Therefore, the thermal expansion of the color selecting member causes no misregistration in the peripheral area nor non uniform display between the central area and the peripheral area. This enables complete prevention of occurrence of defective display such as misregistration or display failure, thereby achieving extremely high picture quality, especially in cathode ray tubes which often has a problem of misregistration in the horizontal direction, such as a cathode ray tube with a large screen or a cathode ray tube for HDTV having a screen in landscape orientation of an aspect ratio of 16:9.
Other and further objects, features and advantages of the invention will appear more fully from the following description.